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September 1, 2012

Bakersfield Night Sky – September 1, 2012
By Nick Strobel

The Dawn mission finished scientific observations of Vesta on August 26th and is now spiraling away from Vesta to begin its three-year journey to the dwarf planet Ceres. It will arrive at Ceres in February of 2015. Vesta and Ceres are the two most massive members of the asteroid belt. Vesta is made of bright material on its surface and it can approach close enough to the Earth that we can sometimes see it as a dim spot without a telescope. No, Vesta will never get close enough to the Earth to crash into it. Normal asteroids are just chunks of debris left over from the solar system's formation and are important for studying for that reason. Vesta is unusual in that it is a layered, planetary building block with an iron core—the only known surviving protoplanet from the solar system's formation 4.6 billion years ago. It has a crust, mantle, and iron core like a planet.This layering formed when Vesta had a subsurface magma ocean—when Vesta was almost completely melted so its rock was liquid.

Dawn confirmed that three classes of meteorites that fell to Earth did in fact come from Vesta. Those types of meteorites account for about 6 percent of all meteorites falling on Earth, making Vesta one of the largest single sources for Earth's meteorites.

Vesta's topography is steeper and more varied than originally expected. Some of the crater walls are almost vertical instead of sloped like those on the Earth, Moon, and other worlds. It has a huge central peak in one of its impact basins that is much higher and wider, relative to crater size, than the central peaks of craters found on other bodies in the solar system. Two of the largest impact basins on Vesta are much younger than the impact basins found on the Moon. That's geologically speaking of course. The youngest impact basin on Vesta is about a billion years old while the Moon's impact basins, including the ones making the dark, smooth maria are about 3.8 billion years old.

Those are the major findings so far, but there will be other discoveries made as scientists continue analyzing data from the framing camera, visible & infrared spectrometer, gamma ray and neutron spectrometer, and the gravity science experiment. The camera gives us the images, the spectrometers tell us the composition of the surface materials and just below the surface, and the gravity science experiment probes the interior structure of the asteroid.

The Dawn team will be having a Hasta la Vesta party on September 8th. You can connect with Dawn team members and others interested in the Dawn mission in real time in a Dawn Mission Google+ Hangout. Listen to mission stories and get your questions answered that you submit via email, Facebook, or Twitter. The Google+ Hangout will take place from noon to 2 PM on September 8th. See the Dawn website at http://dawn.jpl.nasa.gov for more details.

On another world, the Mars Science Laboratory rover, aka "Curiosity", has made its first movement from where it landed and it tested its laser that sends a series of 1 megawatt pulses to vaporize part of a rock in order to find out the rock's composition from a distance. Each pulse lasts just five one-billionths of a second so just a tiny part of the rock is vaporized. (Sorry, no blasters here sci-fi fans.) It is able to use the laser on rocks up to about 23 feet (7 meters) away. The laser is part of the ChemCam instrument in what looks like the single eye of the head of Curiosity. The rest of ChemCam is a camera that can see details 5 to 10 times better than the cameras on the Mars Exploration Rovers. ChemCam will enable Curiosity to rapidly identify rocks it should explore up close with its other instruments.

The MSL team is still running Curiosity through its paces to make sure all of the systems on this most advanced craft to land on Mars are functioning correctly and are carefully calibrated. All of the check and cross-checking of the science instruments and mobility system is expected to take about a month so should be about done by the time this column appears in print.

Returning home, the early morning pre-dawn sky holds some beautiful sights. The first chart below shows the view at 5:30 AM. The two very bright planets, Venus and Jupiter, are visible in the east with Jupiter about two-thirds of the way up in the sky and brighter Venus down closer to the horizon. Jupiter is poking along between the horns of Taurus while Venus moves much more quickly. Tomorrow morning Venus will be next to the head of the Gemini twin Pollux but near the end of next week, it will be at the heart of Cancer. The Moon will join the scene by next weekend. On September 8th, the Moon will be at third quarter phase and just below Jupiter. People farther south than we in South America will see the Moon cover up (occult) Jupiter just before sunrise. As the Moon speeds along, we will see less and less of its daylit side facing us so the crescent phase will be waning (getting thinner and thinner). The attached chart shows that the Moon will catch up to Venus on September 12th when a very thin crescent Moon will be just below bright Venus—a nice view in binoculars! The first chart below also shows that the Orion constellation will be halfway up in the eastern sky by 5:30 AM.

This evening look in the northwest for the Big Dipper part of Ursa Major, the big bear. As shown in the second chart below, extend the arc of the handle of the Big Dipper to the bright star Arcturus at the foot of Bootes. By 8:30 PM, orangish Arcturus will be about a third of the way up in the western sky. Closer to the western horizon you will be able to see a triangle of bright points. The left point of the triangle is orange-red Mars, the upper right point is Saturn, and the lower right point is the star Spica in Virgo. Mars is moving fast enough that by next weekend, it will be right next to Libra. Mars is also moving fast enough on our sky that it will set about 2 hours after sunset all the rest of the year. The Sun will catch up to pokey, more distant, Saturn, so by the end of the month, Saturn will be lost in the evening twilight glow. This evening in the east will be the almost full Moon rising, just one day past full phase. Very high in the west up above kite-shaped Bootes, see if you can pick out the bowtie shape of the central part of Hercules. It will be almost at the zenith, which is the point directly overhead.

Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com

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